The American Film Institute describes some of the history of this gem of a surrealist silent short film:
This is the first film version of The Wizard of Oz, and appears to have been inspired by the 1902 Broadway musical based on L. Frank Baum's novel, because the character of Imogene, the cow, which was not in the original book, had replaced Toto in the play in order that the production would not have to rely on a trained dog.
A column in the 8 Jan 1910 Moving Picture World announced that the Selig Polyscope Company had placed Frank Baum, "the 'Wizard of Oz' man," under contract as a producer.
The 22 Jan 1910 Moving Picture World announced that Selig was issuing "beautiful four-colored lithographed posters by the Russel-Morgan Company in order that the exhibitor may make a special feature" of the film.
See also Selig Polyscope's sequels, Dorothy and the Scarecrow in Oz and The Land of Oz (both 1910).
The George Eastman House restored thirteen minutes of The Wonderful Wizard of Oz, not including the closing credits.
The Wonderful Wizard of Oz (1910) [American Film Institute]